Jump to main content
Jump to site search

Issue 23, 2002
Previous Article Next Article

One-electron reduction of some indole derivatives: Effect of 5-hydroxy substitution

Author affiliations

Abstract

The reactions of eaq with 3-substituted indole derivatives and their 5-hydroxy analogues viz., tryptamine, and 5-hydroxy tryptamine (serotonin); tryptophan and 5-hydroxy tryptophan; tryptophol and 5-hydroxy tryptophol; and also tryptophanol were studied using the pulse radiolysis technique. The transient spectra in all these cases showed maximum absorption at 345–350 nm, attributed to the indolyl radicals. The indolyl radical spectra of tryptamine, tryptophan, tryptophol and tryptophanol did not change significantly with pH, whereas the absorption maximum of the radical spectra of 5-hydroxy tryptamine, 5-hydroxy tryptophan and 5-hydroxy tryptophol changed into a broad red-shifted absorption at 375–380 nm in the alkaline region. By following these absorption changes as a function of pH, the radical pKa of 9.3, 9.6 and 9.0 respectively, were estimated for 5-hydroxy tryptamine, 5-hydroxy tryptophan and 5-hydroxy tryptophol. The indolyl radicals at pH 7 decayed by second order radical–radical reactions with 2k values of 0.6–2.0 × 109 dm3 mol−1 s−1 and the radicals were found to be reducing in nature. They reduce methyl viologen (MV2+) with rate constants of 1.5 to 6.4 × 109 dm3 mol−1 s−1. The indolyl radicals react with oxygen with rate constants of 0.6–3.3 × 109 dm3 mol−1 s−1. While the radicals from tryptamine, tryptophan, tryptophol and tryptophanol on reaction with oxygen did not produce any new absorption, the 5-hydroxy substituted compounds produced a new absorption in the 300 to 500 nm region with an absorption maximum at 400–410 nm, similar to indoloxyl radicals. The rate of formation of these newly absorbing radicals matched well with the decay of the indolyl radicals in the presence of oxygen and was independent of the pH and parent indole concentration. The oxygen radical adducts/indoloxyl radicals of all these indolyl radicals oxidise TMPD with rate constants of 1.5–8.7 × 107 dm3 mol−1 s−1.

Back to tab navigation

Publication details

The article was received on 05 Aug 2002, accepted on 07 Oct 2002 and first published on 28 Oct 2002


Article type: Paper
DOI: 10.1039/B207618G
Citation: Phys. Chem. Chem. Phys., 2002,4, 5872-5877
  •   Request permissions

    One-electron reduction of some indole derivatives: Effect of 5-hydroxy substitution

    G. H. Naik, K. Indira Priyadarsini and H. Mohan, Phys. Chem. Chem. Phys., 2002, 4, 5872
    DOI: 10.1039/B207618G

Search articles by author

Spotlight

Advertisements